A speed/rotation sensor of an electrical motor typically comprises an optical or magnetic disk mounted on the shaft of the motor. An optical disk contains a series of light reflective or magnetic bars that allows electrical pulses to be generated. Noise introduced by dust and scratches located on an optical disk of a speed sensor of a motor may create inaccurate processing by downstream circuitries, including but not limited to false direction detection that may lead to inaccuracy in system positioning and/or additional delay in positioning.
Small dust particles can produce small spurious pulses in the electrical pulses, which can be easily filtered using conventional filtering circuitry. Large dust particles and scratches, however, may produce spurious pulses having larger duration, which are more difficult to suppress using conventional filtering circuitry designed to filter small spurious pulses.